This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 20 |
| 3 | 106 |
| 4 | 560 |
| 5 | 2914 |
| 6 | 14960 |
| 7 | 76066 |
| 8 | 384320 |
| 9 | 1933954 |
| 10 | 9707600 |
| 11 | 48653026 |
| 12 | 243613280 |
| 13 | 1219116994 |
| 14 | 6098749040 |
| 15 | 30503261986 |
| 16 | 152544909440 |
| 17 | 762810444034 |
| 18 | 3814310107280 |
| 19 | 19072324590946 |
| 20 | 95363945904800 |
| 21 | 476826699947074 |
| 22 | 2384154414150320 |
| 23 | 11920834820287906 |
| 24 | 59604362362631360 |
| 25 | 298022376621898114 |